The decrease in breast feeding in infants in the U.S. over the past 30 years has been reflected in Native American populations in a shorter period of time. This study is intended to document changes in breast feeding among the Pima Indians living on a reservation in Arizona and to compare the health effects of breast and bottle fed infants over the past 20 years. The availability of centralized health records at the Sacaton Hospital of the Indian Health Service and the relative lack of mobility of the population makes this an excellent source for the study of this issue of current national concern.